Our aim is to characterize the cellular differentiation associated with premalignant changes in respiratory epithelium. This has been studied at the level of: A. Neuroendocrine differentiation. We have demonstrated that 15% of non- small cell lung carcinomas (NSCLC) express multiple neuroendocrine (NE) features. Our results indicate that these tumors are sensitive to chemotherapy. The role of NE differentiation in non-neoplastic epithelium is investigated. B. Peripheral airway cell differentiation. We found 30% of the 400 NSCLC tumors examined to be positive for at least one of the peripheral airway cell (PAC) markers SP-A and CC10. They also formed a clinically distinct subset. Characterization of NSCLC cell lines expressing PAC markers is in progress. In order to define premalignant lesions, we are studying the response of PACs in non-neoplastic lung to pulmonary carcinogens, including tobacco specific nitrosamines. C. Clara cell specific protein (CC10) also known as a PCB(a potent carcinogen)-binding protein. We have demonstrated that non-ciliated secretory cells, which are progenitor cells for the epithelium and NSCLC, express high levels of CC10, while only 10% of NSCLC are positive for CC10. Our preliminary results showed that in the presence of smoking related atypia the patterns of CC10 mRNA expression in non-neoplastic human lung were affected both in larger airways and alveoli, while changes in smaller airways were minimal. Changes involved both intensity and cellular distribution of mRNA. Further studies are in progress. D. Oncogene expression. We have found overexpression of c-myc in a high number of NSCLC as well as in the progenitor cells in human lung by in situ hybridization. In a cohort of 120 NSCLC patients, overexpression of p53 tumor suppressor gene was correlated with shorter survival in a subset of patients. Molecular analysis of the potentially prognostic mutations, and the mutations in premalignant changes in the surrounding non-neoplastic lung is in progress. The significance of the project is that the results will provide a rational basis for innovative approaches for early detection and intervention in human lung cancer.